The present invention relates to a speaker and a speaker system employing a plurality of the speakers.
In a known speaker, a cone-shaped diaphragm is attached to a distal end of a voice coil bobbin and a damper is fixed to an outer periphery of the voice coil bobbin. An edge member is provided at an outer peripheral portion of the cone-shaped diaphragm, while a voice coil is held in a magnetic gap of a magnetic circuit.
In the known speaker of the above described arrangement, when an electrical signal is applied to the voice coil, a driving force produced in the voice coil is transmitted to the voice coil bobbin so as to vibrate the cone-shaped diaphragm secured to the distal end of the voice coil bobbin. The cone-shaped diaphragm is supported by the damper fixed to the outer periphery of the voice coil bobbin and the edge member. Linearity of a supporting force of the damper and the edge member, which support the cone-shaped diaphragm poses a problem, especially when reproducing in a low-pitched zone, and forms a main cause of the production of harmonic distortion.
In order to improve the linearity of the supporting force of the support members, various shapes have been proposed. As a result, an edge member which is formed into a rolled shape having a semicircular cross section is most popularly used at present. By combining this edge member with a damper having a corrugated cross section, linearity of the supporting force of the support members has been improved substantially. FIG. 25 shows vibration states of the rolled edge member. In FIG. 25, reference numeral 7 denotes the cone-shaped diaphragm, reference numeral 9 denotes the rolled edge member and reference numeral 10 denotes a frame to which an outer periphery of the edge member 9 is secured. In FIG. 25, character A represents a neutral vibration state prior to application of the electrical signal to the voice coil, in which the rolled edge member 9 is disposed at a neutral point, character B represents a forward vibration state in which the rolled edge member 9 is forwardly vibrated through an amplitude I from the neutral point and character C represents a rearward vibration state in which the rolled edge member 9 is rearwardly vibrated through the amplitude I from the neutral point. Since the rolled edge member 9 is vibrated through the amplitude I forwardly and rearwardly from the neutral point in the forward and rearward vibration states B and C, respectively, as described above, the motion of the edge member 9, acting as the support member for the cone-shaped diaphragm 7, does not include a non-linear component.
In FIG. 25, when the rolled edge member 9 is vibrated from the neutral vibration state A to the forward vibration state B, the edge member 9, vibrating together with the cone-shaped diaphragm 7, displaces a quantity U1 of air. Meanwhile, when the rolled edge member 9 is vibrated from the neutral vibration state A to the rearward vibration state C, the rolled edge member 9 displaces a quantity U2 of air. Since the rolled shape of the rolled edge member 9 is deformed between the forward and rearward vibration states B and C, the quantities U1 and U2 of air become different from each other.
Sound pressure characteristics of the speaker are proportional to a sum of a quantity of air displaced by the cone-shaped diaphragm 7 and a quantity of air displaced by the edge member 9. However, in the known speaker, since the quantities U1 and U2 of air displaced by the edge member 9 in the forward and rearward vibrations become different from each other, as described above, secondary harmonic distortion is likely to be generated when reproducing in the low-pitched zone.